DESCRIPTION Understanding the molecular basis of neuronal morphogenesis is important for addressing various neurobiological questions, from the establishment of a functional nervous system to the structural plasticity of neurons involved in learning and memory. To study how neurons acquire their complicated morphology in the Drosophila central nervous system, a novel genetic mosaic system has been developed for specifically labeling the morphology of genetically altered neurons in an otherwise wild type background. Using this newly developed system, one can closely follow the morphogenetic process of individual wild type or mutant neurons. To elucidate further the molecular mechanisms of neuronal morphogenesis, various aspects of cytoskeleton organization in developing wild type of mutant neurons will be examined with single cell resolution by using different markers in this new genetic mosaic system. Additionally, development of the mushroom body, especially regulation of neuroblast proliferation and reorganization of neurons during metamorphosis, will be investigated, which is important for future genetic screening of noel genes involved in mushroom body development. Cause of the essential role of the mushroom body in learning and memory, this study will also help to elucidate the molecular mechanisms of learning and memory.